A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Lithography was traditionally undertaken on rigid substrates and/or wafers. While this still continues, in more recent years other applications for lithography have become more popular. For example, recently, applications such as flexible electronics and flexible displays have caused a worldwide research effort on the use of lithographic processes (especially batch processes) on flexible substrates. The fact that optical lithography (and imprint lithography) is a mature technology on rigid substrates makes it a good choice for use in applications which use flexible substrates. However, the translation of optical lithography (and imprint lithography) on rigid substrates to optical lithography (and imprint lithography) on flexible substrates is not straightforward. It may be difficult when trying to use optical lithography (and imprint lithography) to apply patterns to flexible substrates due to the flexible nature of the substrates. Being flexible, the substrates are more susceptible to out-of-plane deformation due to, for example: contamination between the flexible substrate and a surface on which the flexible substrate lies; the flatness of the surface on which the flexible substrate lies; or the flatness of an intermediate layer located in between the flexible substrate and a support structure, for example a glue layer.
It is desirable to provide, for example, an apparatus and method which obviates or mitigates one or more of the problems of the prior art, whether identified herein or elsewhere.